1. Field
The present invention relates generally to wireless communications and more specifically to multi-antenna receive diversity in a wireless communication system.
2. Background
Multi-antenna receive diversity refers to processing multiple received signals in multiple receive chains in a wireless communications device. At least two antennas provide two different input signals to a receiver unit, thereby providing received signal diversity to the communications link. Specifically, the multiple antennas provide spatial diversity as each multi-path appears differently at each antenna. Therefore, the effects of multipath fading are not strongly correlated among the receive paths. As a result, receive diversity improves call and data transmission quality and also increases network capacity.
The outputs of the multiple receiver chains are combined in order to provide a better estimation of the symbols prior to decoding. Combination methods known in the art include, but are not limited to, Minimum Mean Squared Error (MMSE) combining, maximal-ratio combining, equal-gain combining, and selection combining. The main drawback of multi-antenna receive diversity is that each receiver chain expends power, particularly in the Radio Frequency (RF) and analog portions of the chain.
Multi-antenna receive diversity has the ability to increase the forward link capacity significantly. The capacity increase may be capitalized as higher throughput, lower base station transmit power, lower Frame Error Rate (FER), or a combination thereof. One drawback of receive diversity is the power cost of implementing and operating such receivers. In addition, the benefits of receive diversity may not always be utilized or even needed.
There is a need in the art for control methods and apparatuses to use multi-antenna receive diversity when the benefits, such as greater link capacity, higher throughput, lower transmit power, and lower error rate, are available, and not to use multi-antenna receive diversity when the benefits may not justify the higher power cost. Thus, there is a need to control receive diversity to optimize the tradeoff between the benefits of receive diversity and the power consumption of receive diversity in a wireless communications device.